Hitherto, radiation images, such as X-ray images have been widely used for diagnosis of disease conditions in the medical site. In particular, since, radiation images produced by a combination, system of an intensifying screen and an X-ray film have high sensibility and high quality, such a combination system has been, used as a common imaging system in a medical site for a long time.
However, information by these radiation images is so-called analog image information, and cannot be applied to free image processing or instant electrical transmission as with digital image information which has been developed in recent years.
For this reason, in recent years, digital type image detecting devices represented by computed radiography (CR), flat, panel type radiation detector (FPD), and the like have been employed.
The digital type X-ray image detecting devices include a direct type and an indirect type.
As the direct type, for example, X-ray image detecting devices employing solid-state imaging elements (CCD, CMOS, etc.) are known, and as the application, these devices are used for industrial non-destructive inspection and dental radiography in which they are inserted in mouths so as to take still images in the mouths.
The above devices have been developed specifically in the dental diagnosis application remarkably. For example, a small device for use in a mouth has been used in a panoramic photography and Cephalo-graphy in place of film.
In the indirect type, a scintillator panel including a phosphor layer containing a phosphor is used to convert once X rays into visible light, the visible light is converted into electrical charge signals by a flat light receiving element including photodiode, CCD, CMOS and the like, and the electrical charge signals are led to a charge accumulation capacitor.
As compared with the direct type, since the indirect type is simple and has a high sensitivity, it has been used in the wide application.
As a phosphor layer used for the indirect type scintillator panel, phosphor layers containing phosphors which include alkali halides, such as CsBr and CsI, as a base material and are activated with. Eu, Tl, etc. may be used in many cases, because they shows high brightness and high sharpness. Among the X-ray image detecting devices, a flat radiation image sensing device (hereafter, referred to a flat panel detector, or simply referred to FPD) provided with a scintillator panel having a phosphor layer formed by gas phase methods, such as evaporation has been used suitably.
The scintillator panels provided with a phosphor layer formed by gas phase methods, such as evaporation, have the above advantages. However, in the case where the phosphor layer is formed by, for example, evaporation by use of a common substrate, it may be difficult to cut out fee phosphor layer after the evaporation. Accordingly, in order to manufacture a FPD, it is obliged to use a substrate with a size corresponding to the size of the FPD to be manufacture and to form a phosphor layer on the substrate.
In that case, there is a problem that a region (image formation impossible region) incapable of being used for an image formation occurs in a peripheral edge portion of a scintillator panel due to unevenness at the time of evaporation.
On the other hand, in recent years, with the enlargement of an application range of FPD, requests to make a FPD thinner and to enlarge an area of a scintillator contributing image formation increase.
Namely, with the popularization of a small size detector configured to be inserted in a mouth so as to photograph in the mouth in the field of dentistry, smaller and thinner detectors are requested. At the same time, in the smaller and thinner detectors, in order to increase an imaging area in the used area of a FPD, it is requested to reduce an area which, occurs in a peripheral portion of a scintillator panel and cannot be used for image formation.
From the viewpoint of effective utilization of property, such as a photographing stage, a photographing bed, and the like which are widely employed in medical facilities for use in a combination system of an intensifying screen and an X-ray film, a flat panel detector is requested to be made in a cassette size in the combination system of an intensifying screen and an X-ray film. In addition, from the above viewpoint, it is request to make a FPD thinner and to increase an image forming area of a scintillator.
In order to solve the problem of this region incapable of forming images, for example, in the pamphlet of International Publication No. 04/079396, a method of attaching a substrate to an auxiliary base board beforehand is proposed. However, since it is necessary to prepare a substrate of a required size before vapor deposition and to cover the substrate together with the auxiliary base board with an organic film, the method lacks efficiency.
Further, in a known method, a scintillator panel is prepared by forming a phosphor layer on a substrate made of a polymeric material via a deposition method and cut out via a specific cutting method (refer to Patent Document 1). However, the simple application of this known method is insufficient for the above requests.
On the oilier hand, since the CsI-based scintillator (phosphor layer) has a deliquescent property, it has a defect that the characteristic deteriorates over time. In order to prevent fee deterioration over time, it is proposed to form a moisture-proof protective layer on the surface of the CsI-based scintillator (phosphor layer).
Then, for example, in another known method, the top and side surfaces of a scintillator layer (phosphor layer) and the scintillator layer outer peripheral portion of a substrate are covered with a poly-paraxylylene resin (for example, refer to Patent Document 2). Further, in another known method, at least a surface of a scintillator layer opposite to a side facing to a substrate and a side surface are covered with a transparent resin film with a moisture transmission rate less than 1.2 g/m2·day (for example, refer to Patent Document 3). With these protective layers, a high vapor-proof property can be attained.
Furthermore, in order to couple a scintillator panel to a surface of a flat light-receiving element, the scintillator panel is needed to be brought, in pressure contact with the light-receiving element with a proper pressure. Then, in another known method, a cushion member is disposed between a protective layer and the scintillator panel.
That is, at the time of fabrication of a flat panel detector, a scintillator panel and a cushion member are stacked sequentially on a light receiving element disposed in a housing body, and thereafter, a protective layer is secured in the housing body, thereby fabricating the detector.
However, in this case, it is necessary to keep balance against the following problems.
For example, in the case where the moisture proof property of a detector housing body is insufficient, a high moisture proof property is required for a moisture proof protective layer on the surface of a scintillator (phosphor layer). In the case where the pressure of a cushion member is too strong, the tip portions of phosphor crystals in a columnar crystal configuration are made to collapse, and the contrast of a radiation image decreases. In contrast, in the case where the pressure of a cushion member is weak, when a FPD is oriented downward, or due to vibration, a positional deviation takes place between the surface of a scintillator panel and the surface of a flat light-receiving element. As a result, signal correction accuracy in each pixel of the flat light-receiving element decreases and the granularity and sharpness of the obtained image deteriorate.
Further, there is also a problem that defects tend to easily occur on a flat light-receiving element or a phosphor layer due to friction, between a scintillator panel and a flat light-receiving element caused by movement and vibration of a FPD device.
In order to solve above problems, a method of fixing a scintillator panel and a flat light-receiving element with an adhesive agent (for example, refer to Patent Document 4), a method of pasting them with a matching oil (for example, refer to Patent Document 5) and the like are proposed.
However, in order to secure a moisture proof property since the thickness of an adhesive agent is also added to a thick protective layer for, there is a problem that sharpness deteriorates.
In order to avoid this problem, a method of forming scintillator directly on an image sensor by deposition, and a method of using a medical intensifying screen, which has flexibility regardless of low sharpness, as substitution are conducted generally. Further, Japanese Unexamined Patent Publication No. 2008-107279 Official Report discloses an example that the shape of a scintillator panel is made to conform to the shape of the surface of a flat light-receiving element by forming a scintillator on a flexible resin substrate by vapor deposition so as to obtain uniform sharpness on all over the tight receiving surface of a flat panel detector.
However, these methods are also insufficient for the above requests to make the flat panel detector thinner and to reduce a non-imaging region on peripheral portions of a scintillator plate.